Selective laser sintering technology for customized fabrication of facial prostheses
Guofeng Wu DDS, PhDa, Bing Zhou DDSb, Yunpeng Bi DDSc and Yimin Zhao DDS, PhDd, ,
aLecturer, Department of Prosthodontics. School of Stomatology, FourthMilitaryMedicalUniversity (FMMU), Xi’an, China
bDoctoral student, Department of Prosthodontics. School of Stomatology, FourthMilitaryMedicalUniversity (FMMU), Xi’an, China
cGraduate student, Department of Prosthodontics. School of Stomatology, FourthMilitaryMedicalUniversity (FMMU), Xi’an, China
dProfessor and Dean, School of Stomatology. School of Stomatology, FourthMilitaryMedicalUniversity (FMMU), Xi’an, China
Available online 25 June 2008.
Traditionally, wax or clay sculpted patterns have been used in the development of facial prostheses. New advances in rapid prototyping technologies have demonstrated significant advantages compared to more conventional techniques for fabricating facial prostheses. The use of selective laser sintering technology described in this report is an alternative approach for fabricating a wax pattern for a partial nasal prosthesis. This new approach can generate the wax nasal pattern directly and reduce labor-intensive laboratory procedures. (J Prosthet Dent 2008;100:56-60)
Article Outline
Technique
Discussion
Summary
Acknowledgements
References
Over the past decade, advances in rapid prototyping (RP) have continued to evolve, resulting in the development of new techniques which have been applied to the fabrication of maxillofacial prostheses.Rapid prototyping is used to describe the customized production of solid models using 3-dimensional (3-D) computer data, and has resulted in fabrication technologies such as stereolithography (SLA, the first rapid prototyping technique), fused deposition modeling (FDM), and, more recently, selective laser sintering (SLS).1 Currently, SLA technology is the most popular RP technology applied in the field of maxillofacial prosthetics, and has demonstrated significant advantages.[2], [3] and [4] The SLA method uses liquid photopolymer resins that are solidified by a laser to generate maxillofacial prototypes. However, a major disadvantage of SLA technology is that it can only fabricate resin prototypes of facial prostheses, which cannot be directly used for laboratory processing[5] and [6]; thus, the technicians or anaplastologists must replicate the resin prototypes in a wax pattern using conventional dental impression/replication methods. Obviously, these additional processes result in significantly greater complexity, require more time, and likely result in greater inaccuracies.
A method to eliminate the required replication of SLA resin patterns is to use SLS technology, which enables the direct fabrication of wax prototypes for development of facial prostheses. In the last few years, SLS technology has been used in the medical field. This approach enabled replication of a temporal bone model suitable for dissection training and education.7 Fabrication of a 3-D laryngeal model for laryngeal surgery with the use of SLS has also been reported.8 However, the literature to date has rarely reported using SLS technology for fabrication of maxillofacial prostheses.
The SLS process was developed at the University of Texas in Austin, Tex, and is a patented process (DTM Corp, Austin, Tex). Unlike SLA, SLS technology generates direct solid wax patterns instead of resin patterns from wax powder or polystyrene powder.9 It is a free-form fabrication method, creating patterns using thermal fusing (sintering) of powdered materials. The SLS models are generated directly from 3-D computer data converted to STL files, which are then sliced into thin layers (typically about 0.1 mm/0.004 inches) using the associated software.9 The laser sintering machine produces the models on a moveable platform by applying incremental layers of the pattern material. For each layer, the machine lays down a film of powdered material with an accurate thickness (approximately 0.1 mm/0.004 inches). The laser then melts selected areas so that they conform to the previous layer. The platform then moves down the preprogrammed layer thickness, a fresh film of powder is laid down, and the next layer is melted with exposure to the laser source. This process continues, layer by layer, until the pattern is completed. The manufacture time is reduced and its cost is less, compared to the SLA approach. The precision of the SLS process has been reported to be within 10 μm.1 This article describes the use of SLS technology to create a wax nasal pattern.
Technique
- Examine the patient and discuss the treatment options ( Fig. 1)
High-quality image (109K)Fig. 1.Patient with partial nasal defect.
2. Seat the patient upright in a dental chair to minimize any movement. Scan the patient's face with an optical digitizing scanning system (3DSS-STD-II; DigitalManu Corp, Shanghai, China) for 4 seconds to obtain 174,541 data points.
3. Transfer and save the data to a computer (Pavilion a6355cn; Hewlett-Packard, Palo Alto, Calif) as an ASCII file. Process the data with reverse engineering software (Geomagic Studio 10.0; Geomagic, Research Triangle Park, NC).
4. Generate a CAD model of the patient's face (Model A) (
Fig. 2, A). Triangulate the topographic point cloud data to reconstruct the surface profiles. Connect each data point to its 2 nearest adjacent points to form thousands of triangles, which are then interconnected automatically by the software.
High-quality image (260K)Fig. 2.Computer-aided design process for nasal prosthesis. A, Three-dimensional model of patient's face based on digitized data. B, Selected nasal model from 3-D nose bank. C, CAD model of nasal prosthesis prototype.
5. Pick 1 similar nasal model (Model B) (
Fig. 2, B) from a 3-D nose bank (Chinese 3-D Nose Model Database; FMMU, Xi’an, China) to match with Model A. Invite the patient to view the images of the nasal model on the computer screen and express any requests for corrections. Merge the 2 models into 1 file to obtain the data for the development of the nasal prosthesis prototype (Model C) (
Fig. 2, C).
6. Transfer Model A and Model C into physical 3-D models, respectively, using the selective laser sintering system (AFS-360; Beijing Long Yuan - Automated Fabrication System Co, Ltd, Beijing, China). Generate a wax prototype (Model D) (
Fig. 3) with the wax powder (LY-WAX; Beijing Long Yuan - Automated Fabrication System Co, Ltd) from Model C. Create another resin prototype (Model E) (
Fig. 4) from Model A with the polystyrene powder (PSB-1; Beijing Long Yuan - Automated Fabrication System Co, Ltd). Control the fabrication of the model using software (Magics RP 9.5; Materialise Group, Leuven, Belgium).
High-quality image (82K)Fig. 3.Wax model of nasal prosthesis from SLS process.
High-quality image (65K)Fig. 4.Resin model of nasal defect fabricated with SLS process.
7. Place Model D on the patient for modification and correction. Evaluate the contours and marginal fit of the nasal prosthesis.
8. Set Model D on Model E (
Fig. 5), finalize the margins, and add the skin textures to replicate the skin characteristics of the patient.
High-quality image (70K)Fig. 5.Wax nasal pattern with resin model of nasal defect.
9. Process Model D and Model E together, and fabricate the definitive nasal prosthesis in the conventional manner.
10 Invest Model D and E with the dental stone (New Fujirock; GC Lab Technologies Inc, Alsip, Ill) (
Fig. 6) to produce the mold, then heat the flask and remove the wax prototype (Model D). Fill the mold with silicone material (A-2186; Factor II, Inc, Lakeside, Ariz) and polymerize it in a temperature-controlled water bath. Paint the definitive nasal prosthesis with special colorants (Functional Intrinsic Skin Colors Kit and Extrinsic Coloration System; Factor II, Inc, Lakeside, Ariz) and evaluate it on the patient's face (
Fig. 7).
High-quality image (90K)Fig. 6.Flasked wax pattern on resin model.
High-quality image (173K)Fig. 7.Completed partial nasal prosthesis on patient. A, Left-side view. B, Right-side view.
Discussion
The technique described in this article represents an innovative fabrication method that may be advantageous for the patient as well as the maxillofacial prosthodontist. Using the SLS technique, the need for labor-intensive/time-consuming sculpting was significantly reduced because the nasal wax pattern was automatically fabricated by machine. Another advantage of SLS wax is its low cost, which is approximately 60% less than that of the SLA photopolymer resins. The market price of an SLS machine is approximately 75% of the price of an SLA machine. Furthermore, the used wax material can be sterilized by epoxyethane and recycled. The precision of the computerized model allows for satisfactory restoration of the facial contours.
In addition, the SLS machine fabricated the polystyrene resin prototype of nasal defect (Model E) in this study; this model was then processed with an SLS wax pattern for flasking. The SLS resin model was produced directly from the data of 3-D contact-free measurements, which offered the advantage of not distorting the facial tissue, as can occur with more conventional moulage impression techniques. SLS models are precise replicas of the patient's anatomy.11 The technique described demonstrates that the SLS resin prototype was an acceptable substitute for the conventional plaster/stone moulage cast/mold for laboratory processing.
However, the SLS technique has limitations. The existing SLS wax material is designed for industrial use and needs refinement to be suitable for use in the fabrication of maxillofacial prostheses. Currently, the process is also relatively costly due to its limited marketability and expensive equipment. Even with these limitations, SLS technology has begun to make an impact in medicine. SLS and other rapid prototyping techniques have been and will be applied to a wide variety of medical applications. In time, more advanced RP applications will become available in hospitals and clinics, where a large number of patients could benefit from this technology.
Summary
This article describes the use of SLS to produce a wax prototype for the fabrication of a partial nasal prosthesis. This technique may be an alternative to more conventional laboratory techniques for facial prosthesis fabrication and allows direct generation of definitive wax patterns. With the satisfying effect of nasal defect restoration, patients may be effectively rehabilitated and derive emotional and physical benefit from the treatment provided.
Acknowledgements
The authors thank Dr Steven P. Haug and the AmericanAcademy of Maxillofacial Prosthetics for their support of this article.
References
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